1. Field of the Invention
Example embodiments of the present invention relate to a method of forming a phase changeable material layer, a method of manufacturing a phase changeable memory unit, and a phase changeable semiconductor memory device using the same. More particularly, example embodiments of the present invention relates a method of forming a phase changeable material layer including chalcogenide, a method of manufacturing a phase changeable memory unit using the same, and a phase changeable semiconductor memory device using the same.
2. Description of the Related Art
A phase changeable memory device stores information using structural phase changes in certain thin-film alloys that typically utilize one or more elements from Column VI of the periodic table. These alloys are stable in both (a) a crystalline state in which the atoms are arranged in a regular periodic structure and (b) an amorphous state with an irregular atomic structure. The two states have different electrical and optical characteristics and can be switched therebetween by applying a pulse of energy. The crystalline state typically has a low resistance and is highly reflective, and the amorphous state typically has a high resistance and a dull appearance. These phase changeable alloys are referred to as chalcogenide materials and include germanium (Ge), antimony (Sb), and tellurium (Te).
A conventional PVD (physical vapor deposition) process such as sputtering or evaporation deposition is typically used to form a phase changeable material layer such as a mixture of germanium, antimony, and tellurium (GST). However, when using the conventional PVD process, it is difficult to control a growth rate of the phase changeable material layer. Accordingly, the phase changeable material layer formed by the conventional PVD process is typically not dense, and it is difficult to form the phase changeable material layer to have a FCC (Face Centered Cubic) crystallization structure having excellent electrical characteristics.
When forming the phase changeable material layer using the PVD process, the electrical characteristics of the phase changeable material layer deteriorate because it is very difficult to precisely control a composition ratio of the germanium, tellurium and antimony in the GST mixture. Furthermore, the conventional PVD process is very expensive and time consuming, since a deposition rate is slow.